Packaging tacky polyisobutylene rubber in film of compatible styrene-isobutylene copolymer



y 7, 1957 w. J. SPARKS ET AL 2,791,327

P AC G TACKY POLYISOBUTYLENE RUBBER 1N FILM CO TIBLE STYRENE-ISOBUTYLENECOPOLYMER Filed Dec. '7

\Mlliom J. Sparks Francis P Boldw' Raymond G. N erg By Z AttorneyInventors PACKAGING TACKY POLYISOBUTYLENE RUB- BER IN FILM or COMPATIBLESTYRENE-ISO- BUTYLENE COPOLYMER William J. Sparks, Westfield, Francis P.Baldwin, Rahway,

and Raymond G. Newberg, Roselle Park, N. 5., assign- .ors to EssoResearch and Engineering Company, a corporation of Delaware tApplication December 7, 1955, Serial No. 551,704 5 Claims. (31. 206-84)This invention relates to a new article of manufacture and methods ofmaking same, and more particularly, it relates to novel and improvedmethods of packaging plastic materials which are tacky and havesubstantial cold-fiowing tendencies. One particularly importantapplication of the invention is in packaging tacky polyisobutylenesynthetic rubber in films of a copolymer of styrene and isobutylene.

The present application is a continuation-in-part of application SerialNo. 250,688 filed October 10, 1951 which in turn is acontinuation-in-part of application Serial No. 584,622 filed March 24,1945, now U. S. Patent 2, 572,959.

Although the details of the preparation of such synthetic rubber do notconstitute a part of this invention, it may be noted for the sake ofgeneral reference, that such preparation comprises polymerizingisobutylene in the presence of a dissolved metal halide Friedel-Craftscatalyst at a temperature below -40 C. A preferred catalyst is made bydissolving aluminum chloride in ethyl chloride or methyl chloride atroom temperature and then cooling the solution down to the desiredcopolymerization temperature. The reaction is preferably carried out inthe presence of a diluent-refrigerant such as liquid ethylene, andpreferably at a temperature ranging from about 50 C. to -l03 C., theboiling point of liquid ethylene.

The synthetic rubber produced by the above described process is anelastic branched chain linear aliphatic hydrocarbon polymer having amolecular weight ranging from about 27,000 to 300,000 or higher(Staudinger). These synthetic rubbers are essentially saturated. Aserious problem is presented to the rubber industry by the necessity ofpackaging the raw rubber for shipment from the manufacturing plant tothe factories Where the raw synthetic rubber is to be compounded withother materials shaped into the desired articles such as inner tubes fortires for autos, airplanes, etc. Because of the tackiness of this rawsynthetic rubber stock, it sticks to any of the conventional packagingmaterials such as paper bags, cardboard boxes or metal containers, infact so tightly that its removal from such containers requires verytime-consuming, drastic procedures. This tackiness problem isparticularly serious with raw synthetic rubber of the type describedhaving a Staudinger molecular weight in the range of about 27,000 to180,000.

One object of the present invention is to package this synthetic rubberwith a film of wrapping material which will prevent the tacky materialfrom sticking to the paper ormetal container in which it is stored orshipped. Another object of the invention is to provide a packagingmaterial which is physically and chemically compatible with thesynthetic rubber so that after storage and shipment, or at any desiredtime, the wrapper film which is used to prevent the tacky material fromsticking to the outer container may be homogeneously mixed into thesynthetic rubber without deleteriously affecting the desirableproperties of the latter. These and other objects and advantages of theinvention will be apparent to those skilled in the art'from thefollowing specification, particularly when read in conjunction with theaccompanying drawing.

Broadly, the invention comprises wrapping the polyisobutylene syntheticrubber in a thin, flexible continuous, self-sustaining sheet or film ofa substance capable of forming a homogeneous mixture therewith.

One suitable wrapping material is a synthetic copolymer of an aliphaticolefin such as isobutylene and a polymer izable cyclic compound such asstyrene.

A general method of preparing such copolymers is described in U. S.Patent 2,274,749 and this consists in copolymerizing the reactants at atemperature below 0 C. in the presence of an active halidepolymerization catalyst such as boron fluoride or aluminum chloride,with or without the use of a diluent-refrigerant such as liquid propaneetc., and using proportions of reactants which may vary over a broadrange according to desired hardness, melting point, plasticity, etc.However, for the particular purposes of the present invention, thiscopolymer must be prepared under certain relatively narrow conditions.The proportion of aliphatic olefin such as isobutylene used in thecopolymerization should be about 40 to 70% by weight, preferably about45 to 60% by weight, while the proportion of polymerizable cycliccompound such as styrene, should be about to 60%, preferably about to55% by weight, and best results are obtained with even the stillnarrower range of to by weight.

The copolymerization should be carried out at a temperature below 50 0,preferably below C., such low temperatures being obtained byeitherinternal or external refrigeration.

-By thus restricting the proportions of reactants and thecopolymerization temperature, high molecular Weight copolymers areobtained which have an intrinsic viscosity above 0.5 and preferably 0.8or 0.9 or higher. These copolymers are thermoplastic solids which havesuflicient flexibility and toughness particularly in the heat-softenedcondition, to permit ready rolling out into thin sheets or films onsuitable equipment such as the conventional calender used in rubberprocessing.

The copolymerization is effected by mixing the two reactants, with orwithout a mutual solvent, if necessary, such as ethylene,'propane,butane, methyl chloride, refined naphtha, etc., and then after coolingthe reactants to the desired low temperature, adding an active halidecatalyst such as boron fluoride, or activated boron fluoride catalyst(.1% ether added), aluminum chloride, titanium tetrachloride, aluminumalkoxide-aluminum chloride complex-(AlCl3.Al[OC2H5]s) and the like. Ifdesired, such catalyst may be dissolved in a solvent'such as carbondisulfide, a low molecular weight sulfur-free saturated hydrocarbon, alower alkyl halide, e. g., methyl chloride or ethyl chloride or amixture of methyl chloride with butane, at or below the boiling point ofthe catalyst solvent, and then the catalyst solution cooled down,filtered and added to the reaction mixture. Alternative catalystsinclude:

AlC13.A1C12OH, AlBraAlBrzOH AlBrzCLAlOCl, AlBrCl2.AlOBr TiCliAlChOH,TiOClaTiCh, AlB1'3.Br2.CS2

AlBrs, BFa, isopropyl alcohol, BFa solution in ethylene, activated BF3catalyst in ethylene solution, activated -B'Fa catalyst in methylchloride solution. Volatile solvents or diluents, e. g., propane,ethane, ethylene, methyl chloride, carbon dioxide (liquid or solid),etc. may also serve as internal or external refrigerants to carry offthe liberated heat of polymerization. After completion of thecopolymerization, residual catalyst is killed with alcohol, for example,isopropyl and excess catalyst removed by washing the product with waterand preferably also with dilute aqueous caustic soda. The resultingsolid copolymer may range from a relatively stiff plastic mass to a hardtough thermoplastic solid, depending upon the temperature ofpolymerization, the yield of polymer obtained upon the active feed, thetype and concentration of catalyst, the proportion of cyclic reactant inthe feed, and the temperature at which the physical texture is observed.The proportions in which the reactants, e. g., styrene and isobutyl'ene,have actually combined during copolymerization may be determined byinterpolation of a carhon-hydrogen analysis between the limits, forinstance:

Carbon, Hydrogen,

Percent Percent Pure styrene 92.3 7. 7 Pure isobutylene .t 85. 7 14. 3

For convenience and brevity the above described copolymer of acyclicpolymeriz'able material and an olefin or alkene will be referred to as acycalkene copolymer, or more simply a cycalkene. The specific type ofcopolymer made from styrene and isobutylene will similarly be referredto as simply stybutene. The invention will be illustrated as appliedparticularly to stybutene, although it isnot to be limited specificallythereto.

Many resinous and plastic materials either occurring in nature or madesynthetically heretofore are unsuitable for sheeting out into thinself-supporting films because they are either too brittle or have toomuch cold fiow, etc.,

and furthermore, most of the plastics which can be successfully sheetedout into thin self-supporting films are unsatisfactory for the purposeof the present invention, either because they are not physically andchemically compatible with the synthetic rubber type of plastic intendedto be wrapped, and therefore, could not be homo geneously milled intosuch material, or else because they themselves have too much cold flowand tackiness.

For preparing self-supporting films of stybutene for use as a wrapperaccording to this invention, the stybutene, having a high intrinsicviscosity as mentioned above, should be heated well above the softeningpoint, for instance, to a temperature of about 100-l80 C,, preferably ina kneader type mixer to bring the entire mass to a uniform temperatureand plasticity, and then it is sheeted out into a thin film byprocessing on a rubber calender. In this latter operation a three rollcalender may be employed. The center roll is heated to about 220 F. Thetop roll is maintained at a temperature between 250 and 300 F. Thebottom roll is maintained at a temperature of about 80 F. The film isstripped from the middle roll and allowed to cool on the bottom rollthen subsequently rolled automatically on a mandrel. The sheet may thenbe slit or cut to size depending on the application requirements.

In preparing the stybutene film, one may add small amounts of othermaterials to the plastic mass before sheeting it out into film form, asfor instance, small 'aids may be used, or other resinous or plasticmaterials which may be used to slightly modify the physicalcharacteristics of the stybutene film witho'ut greatly affecting thechemical properties thereof or without adversely affecting itscompatibility withthe synthetic rubber or other plastic intended tobewrapped therein. Examples of such various additives, which may be usedin proportioris of 1 to 5% or more, include high molecular WeightpoIybutene (preferably 30,000 to 300,000 molecular weight -Staudinger),'iscsbutylene-polyolefin low-temperature copolymers (preferably 30,000to 150,000 molecular weight Stau'clinger) isobutylene polyolefin-styrenetripoly mers (preferably 10,000 to 100,000 molecular weight Staudinger),high molecular weight sulfurized alkylated phenol (HO(R)CsHa)2S,paratfin wax, high melting point deoiled petrolaturn, vegetable waxes,stearic acid, high molecular weight polymethyl-pentadiene (30,000 to40,000 molecular weight Staudinger), high molecular weight polyethylene,de-proteinized and deashed or' cyclized rubber, cyclized rubber, andaliphatic nitriles that contain 12 to 18 carbon atoms, zinc stea'rate,zinc oxide, sodium stearate, carbon black, etc.

After sheeting out the stybutene into a thin film by rolling,calendering, or any other suitable method, the resulting film which maybe prepared in any desired thickness, but for the present inventionpreferably has a thickness of about .001 inch to .01 inch, or about 1 to10 mils, and preferably about 2 to 4 mils is found to have a smoothsurface, good strength, good flexibility, low permeability to moisturevapor and other gases, low cold flow and little or no surface tack.

In carrying out the invention, it is found that the actual amount ofstybutene film necessary for wrapping the raw synthetic rubber havingcold-flowing tendencies, is relatively very small, ranging for instance,from about 1 to 25 pounds, preferably about 2 to 10 pounds per ton ofsynthetic rubber, the latter preferably being packaged in chunksweighing about 25 to pounds, preferably about 50 pounds each. If chunksof raw synthetic rubber weighing about 50 pounds each are wrapped with astybutene film having a thickness of about 2 mils, the total amount ofstybutene required for the wrapping will be about 4 pounds per ton ofrubber, which amounts to about 0.2% of stybutene by weight. Thinnerfilms can be used with smaller weights of synthetic rubber, andconversely thicker films should be used with relatively larger packagesof synthetic rubber or other plastic.

Although for some purposes such as short time storage and transportationover short distances or requiring only a short time, the plastic havingcold-flowing tendencies and wrapped up in the thin film of stybutene orother cycalkene copolymer having requisite tensile strength, toughnessand non-tackiness, may be used as such i. e., without being placed inany outer container or wrapped in outer wrapping material, it ispreferred to use an outer container such as a corrugated paper carbon,paper or cloth bag, large tin cans, drums, etc., or for some purposeswhere the packages are less subject to mechanical injury from bumpingsolid objects etc., it may be suflicient to cover the stybutene-wrappedsynthetic rubber with ordinary heavy wrapping paper, such as the kraftpaper commonly used for wrapping purposes, such Wrapping being chieflyfor the purpose of keeping the inner package clean' The invention isillustrated in the accompanying drawing in which Figure 1 represents aperspective view of an open corrugated paper carbon containing a largechunk of tacky polyisobutylene synthetic rubber wrapped, except for theopen top, in a thin sheet or film of stybutene copolymer, the Figure 2shows an enlarged section of one of the lower corners of the packageshown in Figure 1, and Figure 3 is a cross section of a package ofsynthetic rubber merely wrapped in a thin film of stybutene without anyouter container or wrapper. In the several figures, like referencenumerals represent like parts.

Referring to Figure l of the drawing, a large piece or chunk of tackyplastic 1, i. e. polyisobutylene synthetic rubber, is shown as wrappedin a thin film of cycalkene copolymer 2, the top of the package beingillustrated open for convenient understanding of the invention, thewrapped tacky plastic being shown as placed in an outer container 3 suchas a corrugated paper carton, also shown open to permit seeing thecontents thereof. It is understood, of course, that for storage andshipment,- the upper flaps of the wrapper 2' will be folded down overthe surface of the plastic 1, and then the lids of the carton 3 will beclosed in the conventional manner.

In Figure 2, which represents a much enlarged vertical section throughone of the lower corners of the package shown in Figure 1, the plastic 1is shown as tightly pressing against the surrounding thin film or sheetof cycalkene copolymer 2, which in turn presses tightly on the bottom ofthe outer container 3 e. g., a corrugated carton. The plastic 1 andsurrounding wrapper 2 may or may not press tightly against the sidewalls and in the bottom corners of the container 3 when first packaged,although during storage and during shipment when the package issubjected to substantial vibration, the plastic 1 tends to flow into thebottom corners and against the side walls of the container 3, therebystretching the thin, tough, but slightly elastic film 2. However, it isfound that even after shipment or after substantial storage, when thecontainer 3 is opened for removing its contents, the plastic 1surrounded by its wrapper 2 will not substantially adhere to the innersurface of the container 3, and can readily be removed withoutdifliculty and in a clean condition.

Figure 3 is a vertical section of a package similar to that shown inFigure 1 except that the plastic 1 is shown merely wrapped in a thinfilm of a cycalkene copolymer 2 without any outer container such asshown in Figures 1 and 2.

The advantages of the invention will be better understood from aconsideration of the following specific example.

Example I Bales of 100,000 mw. polyisobutylene (2" x 4 x 1") werewrapped in 2 mil films of Parapol 8-50 and Parapol 8-60. The bales werethen assembled three in a cardboard carton (the 8-50 wrapped bales inone carton, the 8-60 protected bales in another, and three control baleshaving no protective film coating in a third carton). The cartons werethen placed in an oven maintained at 140 F. Each carton was subjected toa dead weight load of 1.5 #/sq. in. They were maintained in thiscondition for seven days, then removed from the oven, allowed to cool,and examined for sticking and failures. The control without a protectivefilm was found to be stuck so tightly to the carton that it could not beremoved. Those bales wrapped in 8-50 and 8-60 film were easily removedfrom the cardboard cartons with no evidence of sticking. Furthermore,since the Parapols are soluble in hydrocarbon solvents it was found thatthe film coating did not aflect the solution characteristics of thepolyisobutylene. The Parapol 8-60 was a stybutene having a combinedstyrene content of about 60%, and an intrinsic viscosity of about 0.75,which had been made by copolymerizing styrene and isobutylene at -l03C., using as catalyst a 0.5% by weight solution of AlCla in methylchloride, and using 3 volumes of CHaCl as diluent per volume of mixedreactants. The Parapol 8-50 was a stybutene having a combined styrenecontent of 50% and prepared under substantially identicalcopolymerization conditions Instead of actually wrapping the rawsynthetic rubber in the stybutene and then placing the resulting packagein an outer cardboard, paper, cloth, wood or metal container, thestybutene film can first be placed in the empty container and then thecold-flowing plastic can be inserted.

Although it is preferred to use films, it is possible to apply thecoating to the plastic material to be packaged, in other ways. This isespecially true when the plastic packaged is in the form of a bale orblock which is the shape of the package to be used. Alternate methods ofapplying the exterior coating include application of a solution of thestybutene by spraying, brushing or dipping followed by an evaporation ofthe solvent. Instead of a solution of the stybutene an aqueousdispersion thereof can be used and applied in a like manner. When usingsolution or aqueous dispersion, fillers may also be used such as zincstearate, carbon black, etc.

It is not intended that this invention be limited to the specificexamples or modifications which have been described merely for the sakeof illustration, but only by the appended claims in which it is intendedto claim all novelty inherent in the invention, as well as allmodifications coming within the scope and spirit of the invention.

What is claimed is:

1. The method of packaging an isobutylene polymer having tacky,cold-flowing characteristics, which comprises wrapping it in a thin,flexible, continuous, selfsustaining film of a styrene-isobutylenecopolymer.

2. The method of packaging a polyisobutylene synthetic rubber having aStaudinger molecular weight of about 27,000 to 180,000, which compriseswrapping it in a thin, continuous self-sustaining film of astyrene-isobutylene copolymer having an intrinsic viscosity greater than0.5 and having a combined styrene content of about 40 to 60% by weight,and placing the synthetic rubber wrapped with styrene-isobutylenecopolymer in a paper carton for shipment or storage.

3. A package comprising a substantially rigid container, substantiallyfilled with polyisobutylene synthetic rubber having a Staudingermolecular weight of about 27,000 to 180,000, said synthetic rubber beingseparated from said container by a thin film of about 1 to 10 mils inthickness of a styrene-isobutylene copolymer having an intrinsicviscosity greater than 0.5 and having a combined styrene content ofabout 40 to 60% by weight.

4. A package comprising a bag made of fibrous sheet material containingtherein a substantial Volume of polyisobutylene synthetic rubber havinga Staudinger molecular weight of about 27,000 to 180,000, said syntheticrubber being separated from said bag by a thin film of about 1 to 10mils in thickness of a styrene-isobutylene copolymer having an intrinsicviscosity greater than 0.5 and having a combined styrene content ofabout 40 to 60% by weight.

5. A package comprising tacky polyisobutylene synthetic rubber wrappedin a film of about 1 to 10 mils in thickness of a styrene-isobutylenecopolymer having an intrinsic viscosity greater than 0.5 and having acombined styrene content of about 40 to 60% by weight.

No references cited.

3. A PACKAGE COMPRISING A SUBSTANTIALLY RIGID CONTAINER, SUBSTANTIALLYFILLED WITH POLYISOBUTYLENE SYNTHETIC RUBBER HAVING A STAUDINGERMOLECULAR WEIGHT OF ABOUT 27,000 TO 180,000, SAID SYNTHETIC RUBBER BEINGSEPARATED FROM SAID CONTAINER BY A THIN FILM OF ABOUT 1 TO 10 MILS INTHICKNESS OF A STYRENE-ISOBUTYLENE COPOLYMER HAVING AN INTRINSICVISCOSITY GREATER THAN 0.5 AND HAVING A COMBINED STYRENE CONTENT OFABOUT 40 TO 60% BY WEIGHT.